This invention relates generally to a method of maximizing the power output in synchronous motors in field-oriented operation. In particular, the invention pertains to maximizing the power output in induction motors in field-oriented operation at the ceiling voltage while taking into account the reluctance torque in permanent-field synchronous motors.
A synchronous machine or synchronous motor employs a permanent magnet as its field system with a variety of voltage and current regulators to control the torque or power response of the motor. The synchronous motor is characterized by having a large magneto motive force per unit volume. The permanent magnet motor is particularly useful for the drive motor of an electric vehicle. Synchronous motors are additionally useful for the generation of an adjustable torque response.
In order to maximize the power or torque of a permanent field synchronous motor, one must consider three different possible operational ranges. There is an optimal operating range for synchronous motors with internal magnets. Taking into consideration the current and voltage limits for different rotational speeds, there are basically three different operating ranges for maximizing the delivered power and torque. The most favorable operating point will be located within all three operating ranges. The first operating range is the required torque being produced with the smallest possible current or the maximum torque with the maximum current. In this operating range, generally in the lowest rotational speed range, only the current limitation plays a role in producing the torque. Therefore, operating points within this operating range would include the point at which the required torque is produced with the smallest possible current or the maximum torque is produced with the maximum current. The second operating range is when the ceiling voltage is reached, with the additional requirement that the possibility for applying the maximum current to the motor still exists. There are two possibilities within this second operating range with the first possibility being that the synchronous motor operates with maximum current and maximum voltage producing the maximum torque, and the second possibility being that the maximum torque is produced before the maximum current is achieved. The third operating range is when the maximum current can no longer be applied.
The ideal operating point should be located within all of the operating ranges. However, there is no currently available method which can consistently place the synchronous motor at this ideal operating point since the current caused changes of the inductances in synchronous motors are not accounted for. Therefore, there is a need for a method that maximizes the power output in synchronous motors, particularly for permanent-field synchronous motors.
This and other needs are satisfied by the method of the present invention to regulate the torque response of an electric motor or synchronous motor. The present invention is a method for maximizing power output in a synchronous motor, said method comprising the steps of: generating a torque-producing current within said synchronous motor; deriving a field-generating current from said torque-producing current; and deriving an optimal torque-producing current from said torque-producing current and said field-generating current.
In a further embodiment, the present invention is a method for maximizing power output in a synchronous motor, said method comprising the steps of: generating a torque-producing current within said synchronous motor; deriving a field-generating current from said torque-producing current; deriving an optimal torque-producing current from said torque-producing current and said field-generating current; and generating a optimal voltage corresponding to said optimal torque-producing current and using said optimal voltage to control the power output in said synchronous motor.